Controlling etch rate drift and particles during plasma processing

ABSTRACT

The invention is an plasma processing system with a plasma chamber for processing semiconductor substrates, comprising: a radio frequency or microwave power generator coupled to the plasma chamber; a low pressure vacuum system coupled to the plasma chamber; and at least one chamber surface that is configured to be exposed to a plasma, the chamber surface comprising: a YxOyFz layer that comprises Y in a range from 20 to 40%, O in a range from ≦60%, and F in a range of ≦75%. Alternatively, the YxOyFz layer can comprise Y in a range from 25 to 40%, O in a range from 40 to 55%, and F in a range of 5 to 35% or Y in a range from 25 to 40%, O in a range from 5 to 40%, and F in a range of 20 to 70%.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of U.S. Provisional Patent Application No. 61/900,112, filed on Nov. 5, 2013, entitled “Systems and Methods for Controlling Etch Rate Drift and Particles During Plasma Processing”, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

This disclosure is related to methods and systems for processing a substrate and more specifically to methods and systems for controlling etch rate drift and creation of particles during plasma processing.

2. Description of Related Art

Chamber wall materials/coatings are critical in high density plasma process with heavily reactive and corrosive feed gas. Very often, the plasma process is very sensitive to the surface changes of chamber wall materials/coatings with time (or radio frequency (RF) time). Some chamber wall materials/coatings, (e.g. Yttrium based materials or coatings), can run extended RF hours, (for example, greater than thousand RF hours) compared to others, (e.g. anodized Al), which may only run a couple of hundred RF hours. Also, some chamber wall materials/coatings can more easily generate particles compared to other materials/coatings. Furthermore, the surface change of the chamber wall materials/coatings may even change the RF current return or affect the plasma species like radical concentrations, plasma density, or other plasma parameters, which then cause significant process drift, (e.g. etch rate drift), or chamber matching.

So far, yttrium based coatings, mainly Y2O3 coatings have been widely used in plasma process tools as a chamber coating material due to its high resistance to erosion and corrosion, especially in metal or gate etch processes which involve heavily Cl2/O2 or HBr/O2 plasmas. However, in some processes, particles originated from Y2O3 coatings have been recognized to be a big issue especially as the lines or features become smaller and smaller. These particles may cause device and process failure. Also, wafer-less dry clean or wet clean are not the solution to eliminate the particle generation during the plasma process. Alternatively, YF3 coating instead of Y2O3 coatings has been used to suppress the particle generation. However, while it has successfully suppressed the particle generation, other issues appeared. It has been found that the etch rate drifted or decreased significantly with fresh or cleaned chamber walls and it requires extended dummy runs to season the chamber walls in order to have an acceptable and stable etch rate. There are no clear solutions on the Y2O3 particle issue and YF3 etch rate drift issue so far due to lack of understanding of the mechanisms of the particle formation and etch rate drift.

There is a need for an understanding of the mechanism and pathways that cause the particle formation and etch rate drift issues. With this understanding, a system and method for controlling creation of particles and etch rate drift during plasma processing can be developed and implemented.

SUMMARY OF THE INVENTION

The invention is an plasma processing system with a plasma chamber for processing semiconductor substrates, comprising: a radio frequency or microwave power source coupled to the plasma chamber; a low pressure vacuum system coupled to the plasma chamber; and at least one chamber surface that is configured to be exposed to a plasma, the chamber surface comprising: a YxOyFz layer that comprises Y in a range from 20 to 40%, O in a range of ≦60%, and F in a range of ≦75%.

The invention also includes a method for plasma etching semiconductor substrates comprising: positioning a substrate within a plasma processing chamber comprising a surface of Y2O3; flowing process gases comprising HBr and O2; flowing a scavenger gas with the process gas, the scavenger gas comprising CFx. The scavenger gas reacts with H in the plasma to minimize reactions between the H and the Y2O3. The method further comprises controlling a composition of the YxOyFz layer to achieve a target yttrium hydroxide particle generation in the plasma processing chamber and a target etch rate of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts an exemplary graph of mass spectrum data of HBr/O2 using a reference silicon substrate;

FIG. 1B depicts an exemplary graph of mass spectrum data of HBr/O2 using a silicon substrate with photoresist;

FIG. 2A depicts an exemplary graph of the ratio of the optical emission spectrum (OES) signal intensity of hydrogen compared to argon as a function of time while FIG. 2B depicts an exemplary graph of the ratio of the OES signal intensity of bromine compared to argon as a function of time;

FIG. 3A depicts an exemplary graph of the ratio of the OES signal intensity of oxygen compared to argon as a function of time where the O/Ar ratio is from 0.45 to 0.70 while FIG. 3B depicts an exemplary graph of the ratio of the OES signal intensity of oxygen compared to argon as a function of time where the O/Ar ratio is from 0.155 to 0.200;

FIG. 4 depicts the average etch rate (EA) in nanometers for groups of YF3 based chamber wall coatings showing significant etch rate drift;

FIG. 5 depict the formation of OH molecules in a plasma chamber coated with Y2O3 monitored by OES, which is attributed to cause the yttrium hydroxide particles formation;

FIGS. 6A, 6B, and 6C depict the mechanism of the average etch rate (EA) drift associated with the YF3 coating when hydrogen, bromine, and oxygen are presented in the gas composition as a function of time;

FIG. 7 depicts the average etch rate (EA) changes during wafer process and after chamber cleaning;

FIG. 8 depicts a plasma processing chamber for etching a substrate with at least one chamber surface including a YxOyFz layer; and

FIG. 9 is a flowchart illustrating a method of etching a substrate using a processing chamber with at least one chamber surface including an YxOyFz layer in an embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as a particular geometry of a processing system, descriptions of various components and processes used therein. However, it should be understood that the invention may be practiced in other embodiments that depart from these specific details.

Similarly, for purposes of explanation, specific numbers, materials, and configurations are set forth in order to provide a thorough understanding of the invention. Nevertheless, the invention may be practiced without specific details. Furthermore, it is understood that the various embodiments shown in the figures are illustrative representations and are not necessarily drawn to scale.

Various operations will be described as multiple discrete operations in turn, in a manner that is most helpful in understanding the invention. However, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. Operations described may be performed in a different order than the described embodiment. Various additional operations may be performed and/or described operations may be omitted in additional embodiments.

As used herein, the term “radiation sensitive material” means and includes photosensitive materials such as photoresists.

“Substrate” as used herein generically refers to the object being processed in accordance with the invention. The substrate may include any material portion or structure of a device, particularly a semiconductor or other electronics device, and may, for example, be a base substrate structure, such as a semiconductor wafer or a layer on or overlying a base substrate structure such as a thin film. The substrate may be a conventional silicon substrate or other bulk substrate comprising a layer of semiconductive material. As used herein, the term “bulk substrate” means and includes not only silicon wafers, but also silicon-on-insulator (“SOI”) substrates, such as silicon-on-sapphire (“SOS”) substrates and silicon-on-glass (“SOG”) substrates, epitaxial layers of silicon on a base semiconductor foundation, and other semiconductor or optoelectronic materials, such as silicon-germanium, germanium, gallium arsenide, gallium nitride, and indium phosphide. The substrate may be doped or undoped. Thus, substrate is not intended to be limited to any particular base structure, underlying layer or overlying layer, patterned or un-patterned, but rather, is contemplated to include any such layer or base structure, and any combination of layers and/or base structures. The description below may reference particular types of substrates, but this is for illustrative purposes only and not limitation.

FIG. 1A depicts an exemplary graph 10 of mass spectrum data using a reference silicon substrate exposed to a HBr/O2 process gas. The reference silicon substrate can be a bare silicon substrate or silicon dioxide substrate, and the process gas can be a combination of HBr and oxygen. Graph 10 shows the number of counts of H2O related molecules versus the atomic mass units (uma) as measured by a mass spectrometer. The measurement 14 for the reference silicon substrate is indicated by peak H3O+ and exceeds 1,200,000 counts. FIG. 1B depicts an exemplary graph 50 of mass spectrum data of HBr/O2 plasma using a silicon substrate with photoresist. The measurement 54 for the silicon substrate with resist is indicated by peak H3O+ and exceeds 200,000 counts. The traditional Y2O3 coating in processing chambers is usually very stable to ambient conditions and it has very high melting temperature up to 268 degrees C. However, under HBr/O2 high density plasma condition, OH molecule or H and O atoms are generated. These species can react with Y2O3 to form Y(OH)3:

Y2O3+3H2O=2Y(OH)3.

This yttrium hydroxide is very brittle and can form particles from the Y2O3 coating surface.

FIG. 2A depicts an exemplary graph of the ratio of the OES signal intensity of hydrogen compared to argon as a function of time where the H/Ar ratio is from 0.30 to 0.60 while FIG. 2B depicts an exemplary graph of the ratio of the OES signal intensity of bromine compared to argon as a function of time where the Br/Ar ratio is from 3.8 to 5.0, both using a process chamber where a surface is treated with YF3.

FIG. 3A depicts an exemplary graph of the ratio of the OES signal intensity of oxygen compared to argon as a function of time where the 0/Ar ratio is from 0.45 to 0.70 while FIG. 3B depicts an exemplary graph of the ratio of the OES signal intensity of oxygen compared to argon as a function of time where the 0/Ar ratio is from 0.155 to 0.200, both also using a process chamber where a surface is treated with YF3. The increase in the ratios shows that surface recombination rate change of the radicals on the YF3 layer causes an etch rate drift during the plasma processing. It also indicates that YF3 coating layer undergoes a surface composition change during plasma process (surface modification by plasma species reaction with wall).

FIG. 4 depicts graphs 400 of the average etch rate (EA) in nanometers for groups of YF3 based chamber wall coatings showing significant etch rate drift. The group of graphs included in dotted line circle 404 showed significant improvement in average etch rate as the number of substrate used for “seasoning” the plasma processing system increases. Seasoning is a process of processing a blank or bare silicon substrate in an etch or other fabrication process in order to establish a set of stable conditions and achieve the objective of the process. In this case, the objective of the seasoning is to reduce the size and the number of Y(OH)3 particles generated and increase the etch rate to a rate that is within the process expectation.

FIG. 5 depict graphs illustrating the significance of OH peak formation in an Ar/HBr/O2 plasma OES which is an indication of yttrium hydroxide particles generation.

FIGS. 6A, 6B, and 6C depict with graph 600, 610, and 620 the mechanism of the radical drift during seasoning with blank substrate with hydrogen, bromine, and oxygen in the plasma gas composition respectively and where the radical drift is presented as a function of time. Graph 604 depicts a trend line from data points of the hydrogen to argon intensity ratios as a function of time. Trend line 604 indicates that the hydrogen to argon intensity ratios rise as time passes and as more blank substrates are passed through the etching system. Similarly, graph 610 of FIG. 6B depicts a trend line from data points of the bromine to argon intensity ratios as a function of time. Trend line 614 indicates that the bromine to argon intensity ratios rise as time passes and as more blank substrates are passed through the etching system. Similarly, graph 620 of FIG. 6C depicts a trend line from data points of the oxygen to argon intensity ratios as a function of time. Trend line 624 indicates that the oxygen to argon intensity ratios rise as time passes and as more blank substrates are passed through the etching system.

FIG. 7 depicts a graph 700 of the average etch rate (EA) as a function of time. The solid line graph 708 shows the EA in nanometers per unit of time on the Y-axis on the left. Graph 704 starts at time 0 with 90 nm of EA and proceeds upward until time 17, point 716, where the etch rate goes down abruptly due to opening of the chamber for cleaning, designated by time slot 736. Graph 708 reaches a lower etch rate at time 22, 97 nm of EA, point 724 where the etch rate starts going up and levelling off. Similarly, the dotted line graph 704 shows the change of etch rate as a percentage referenced to time 0 on the Y-axis on the right. Graph 704 starts at about 1.8% A at time 0, proceeds with a moderate up-slope until time 17, point 728, where the % A goes down in response to opening of the chamber, designated by time slot 736. Graph 704 reaches a lower etch rate at time 22, at 2% Δ, point 728 where the % A start going up and levelling off at about 4.3% Δ. In summary, FIG. 7 illustrates how the etch rate is affected by the chamber environment.

FIG. 8 depicts an plasma processing system 804 comprising a plasma processing chamber 820 for etching a substrate 816 with at least one chamber surface 808 including a YxOyFz layer 832. The substrate 816 is disposed on a chuck 812 inside the plasma processing system 804. Coupled to the plasma processing chamber 820 are a radio frequency (RF) or microwave power source 824 and a low pressure vacuum system 828. The RF or microwave power generator 824 provides power to create a plasma 836 inside the plasma processing chamber 820. Process fluid treatment 840 is introduced into the plasma processing chamber 820 to create the plasma 836. Process gas 840 may include oxygen containing gases such as O2, CO, CO2, H2O or H2O2 or F-containing gas such as CF4, C4F8, C5F8, F2, or SF6. Other process gases may include HBr, H2, Cl2 and others.

FIG. 9 is a flowchart 900 illustrating a method of processing a substrate using a processing chamber with at least one chamber surface including a YxOyFz layer in an embodiment of the present invention. In operation 904, a substrate is positioned on top of a chuck within a plasma processing chamber, the plasma processing chamber having at least one chamber surface exposed to a plasma, the at least one chamber surface comprising a YxOyFz layer. In operation 908, process gases are flowed into the processing chamber, the process gases, for example, comprising HBr and O2. In operation 912 which is used only when Y2O3 chamber coating is presented and particle formation is the main concern, a scavenger gas is flowed with the process gas. The scavenger gas comprising CFw (fluorocarbon), which can reduce OH or H concentration in plasma. Therefore, H reaction on the Y2O3 coating to form Y(OH)3 can be suppressed. In operation 916, the composition of the YxOyFz layer is controlled to achieve a target reduction of particle generation in the plasma processing chamber and/or a target increase in etch rate of the substrate. The target reduction of the particle generation, can be set at 50% or greater. The target increase in etch rate can be set at a range of 2 to 50% or a range of 15 to 30%.

Some material processing approaches and techniques explain or alleviate the problems described above. The Y2O3 coating can be made dense by reducing the particle size or grain size during plasma spray, getting as close to nanometer-sized Y2O3 particles. Spray particle size can be 1 um or less when applied to the Y2O3. Polished or glass ball blasting can be used to further smooth and increase the density of the coating surface to prevent H2O uptake. Surface roughness (Ra) of the Y2O3 layer may be less than 1.6 um. Pre-coat the Y2O3 surface using SiCl4 or CFx (fluorocarbon) gases to reset the surface or fill the porous portions of the Y2O3 layer. The surface roughness (Ra) may be less than 1.6 um.

Adding small amount CFx (fluorocarbon) into plasma gas recipe; F or C species in HBr/O2/CFw plasma will scavenge the H in the plasma to prevent H reaction on the Y2O3 coating to form Y(OH)3. A surface layer of YxOyFz on the Y2O3 coating using a plasma treatment in CFw or F containing gas. An alternate furnace thermal treatment in F containing ambient, or wet chemical treatment in HF may be performed.

In one embodiment, plasma-spray a layer of YF3 onto the Y2O3 coating to form a multilayer coating. The YxOyFz layer thickness may be less than 10% of the Y2O3 layer thickness. Alternatively, plasma-spray a layer of YF3 onto the Y2O3 coating followed by thermal annealing to form a mixture coating. The YF3 layer thickness may be less than 10% of the Y2O3 layer thickness. In yet another embodiment, simultaneous plasma-spray YF3 and Y2O3 on to a chamber wall parts such that the O composition is less than 60%.

YF3 has a much lower melting temperature, about 1387 C, which enables the plasma-spray YF3 coatings to have a dense and smooth surface. The YF3 coating is also inert to OH attack so no Y(OH)3 compound would form. These are main reason that YF3 has less particle generation issues during the plasma process. However, compared to the Y2O3 surface, surface recombination rate of Br, F, CI and H active species will be much higher on the YF3 surface. The chemisorbed species listed above are not strongly bonded compared to Y—F bond. This bonding situation facilitates the subsequent physisorbed species to recombine with the chemisorbed species to form HBr, Br2, Cl2, F2, etc. These molecular species will then desorb from the surface of the coating(s), which cause radical quenching and reduce the etch rate due to reactants reduction. Furthermore, with continued seasoning and dummy run or a continuous process run, the YF3 coating can be “oxidized” by O radicals, forming a layer of YxOyFz on the YF3 coating. This new layer will gradually reduce the surface recombination rate of reactive species so less radical quenching occurs. As a consequence, the etch rate will gradually increase until the layer of YxOyFz become stable in chemical composition and the recombination rate become small and stable.

The inventor found out that a solid understanding of the mechanisms of the particle generation with Y2O3 layers and the etch rate drift using YF3 layers are needed to resolve these particle generation and the etch rate drift problems. The layer must include the components Y, O, and F in certain ranges. For example, a YxOyFz layer that comprises Y in a range from 20 to 40%, O in a range ≦60%, and F in a range of ≦75%. In another embodiment, the YxOyFz layer can comprise Y in a range from 25 to 40%, 0 in a range from 40 to 55%, and F in a range of 5 to 35%. In yet another embodiment, the YxOyFz layer that comprises Y in a range from 25 to 40%, O in a range from 5 to 40%, and F in a range of 20 to 70%.

In still another embodiment, the YxOyFz layer or a YF3/Y2O3 mixture layer or multilayer is formed by spraying particles of YF3 and Y2O3 with a ratio in a range of 0.1:1 to 10:1. The YxOyFz layer or a mixture layer can be a layer formed on the at least one chamber surface or a liner placed in the plasma chamber.

Several material engineering techniques and approaches were found to assist in solving the particle generation and etch rate drift problems. One alternative is to form a surface layer of YxOyFz on the YF3 coating using a plasma treatment using an O2 containing plasma and/or furnace thermal treatment in O2 containing ambient. Another alternative is to perform a plasma spray of a layer of Y2O3 onto the YF3 coating to form a multi-layer coating. In yet another alternative, the plasma spray can be a layer of Y2O3 onto the YF3 coating followed by thermal annealing to form a mixture coating. Another alternative is prepare the Y2O3 and YF3 in a form that can sprayed or that is in powder form and co-spray the YF3 and Y2O3, varying the ratio of YF3 and Y2O3 in a range from 0.1:1 to 10:1. Another alternative is to spray powder composed of YxOyFz to the chamber wall parts.

Furthermore, there are processes that will improve the properties of the YxOyFz layer. First, the surface of the YxOyFz layer can be pre-coated with SiCl4 or CFx (fluorocarbon) to reset the surface or fill the porous components of the YxOyFz layer. Second, to reduce the surface recombination of the radical, for example, O or F, make the coating dense by using spray particles to reduce the surface area of the YxOyFz layer. Third, the spray particle size of the F-containing spray can be 1 um or less when applied to the Y2O3. Fourth, polished or glass balls can be blasted to make the YxOyFz layer smooth and dense in order to reduce the surface recombination. Fifth, the YxOyFz layer can be heated up to reduce the surface recombination rate of the radicals.

In this invention, x, y, z or w in YxOyFz or in CFw represents the atomic composition percentage in the compounds or molecules.

Although only certain embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention. 

What is claimed is:
 1. A plasma chamber for processing semiconductor substrates, comprising: a radio frequency or microwave power source coupled to the plasma chamber; a low pressure vacuum system coupled to the plasma chamber; and at least one chamber surface that is configured to be exposed to a plasma, the chamber surface comprising: a YxOyFz layer that comprises Y in a range from 20 to 40%, O in a range from ≦60%, and F in a range of ≦75%.
 2. The plasma chamber of claim 1, wherein the YxOyFz layer that comprises Y in a range from 25 to 40%, O in a range from 40 to 55%, and F in a range of 5 to 35%.
 3. The plasma chamber of claim 1, wherein the YxOyFz layer that comprises Y in a range from 25 to 40%, O in a range from 5 to 40%, and F in a range of 20 to 70%.
 4. The plasma chamber of claim 1, wherein the YxOyFz layer was formed with an initial layer of Y2O3 exposed to an F-containing treatment.
 5. The plasma chamber of claim 4, wherein the F-containing treatment included HF, CF4, C4F8, C5F8, F2, or SF6.
 6. The plasma chamber of claim 4, wherein the F-containing treatment is performed in a wet chemical treatment using HF or a plasma treatment using CFw or F.
 7. The plasma chamber of claim 1, wherein the YxOyFz layer was formed with an initial layer of YF3 exposed to an oxygen-containing treatment.
 8. The plasma chamber of claim 7, wherein the O-containing treatment included O2, CO, CO2, H2O, or H2O2.
 9. The plasma chamber of claim 1, wherein the YxOyFz layer was formed with a YxOyFz compound in powder form.
 10. The plasma chamber of claim 1, wherein the YxOyFz layer was formed with Y2O3 in powder form wherein the Y2O3 powder was surface-modified with an F-containing treatment.
 11. The plasma chamber of claim 1, wherein the YxOyFz layer was formed with YF3 in powder form wherein the YF3 powder was surface-modified with an O-containing treatment.
 12. The plasma chamber of claim 1, wherein the YxOyFz layer was formed with a co-spray of Y2O3 in powder form and YF3 in powder form.
 13. The plasma chamber of claim 1, wherein the YxOyFz layer is a layer or a multi-layer that is formed by a plasma spray or a thermal spray comprising YF3 on top of a Y2O3 layer followed by thermal annealing.
 14. The plasma chamber of claim 1, wherein the YxOyFz layer is a layer or a multi-layer that is formed by a plasma spray or a thermal spray comprising Y2O3 on top of a YF3 layer followed by thermal annealing.
 15. The plasma chamber of claim 1, wherein the YxOyFz layer has a surface roughness of less than 1.6 μm.
 16. The plasma chamber of claim 1, wherein the YxOyFz layer or a mixture layer is formed by spraying particles of YF3 and Y2O3 with a ratio in a range of 0.1:1 to 10:1.
 17. The plasma chamber of claim 1, wherein the at least one chamber surface is a liner placed in the plasma chamber.
 18. The plasma chamber of claim 1, wherein percentages of Y, O, and F are controlled to achieve a target etch rate of the substrate and a target particle generation of yttrium hydroxide in the plasma chamber.
 19. A plasma chamber for processing semiconductor substrates, comprising: a radio frequency or microwave power generator coupled to the plasma chamber; a low pressure vacuum system coupled to the plasma chamber; and at least one chamber surface configured to be exposed to a plasma, the chamber surface comprising a YxOyFz layer that comprises F less than or equal to 75%, O less than or equal to 60%, and Y less than or equal to 45%; wherein percentages of Y, O, and F are controlled to achieve a target etch rate of the substrate and a target particle generation of yttrium hydroxide in the plasma chamber.
 20. The plasma chamber of claim 19, wherein the YxOyFz layer or a mixture layer is formed by spraying particles of YF3 and Y2O3 in a ratio in a range of 0.1:1 to 10:1.
 21. The plasma chamber of claim 19, wherein the at least one chamber surface is a liner placed in the plasma chamber.
 22. A method for plasma etching semiconductor substrates comprising; positioning a substrate within a plasma processing chamber comprising a surface of Y2O3; flowing process gases comprising HBr and O2; flowing a scavenger gas with the process gas, the scavenger gas comprising CFx.
 23. The method of claim 22, wherein the scavenger gas reacts with H in the plasma to minimize reactions between the H and the Y2O3.
 24. The method of claim 22, further comprising: controlling a composition of the YxOyFz layer to achieve a target yttrium hydroxide particle generation in the plasma processing chamber and a target etch rate of the substrate. 